bath tub cracked all four corners

If you replace the tub, make sure the supports are the same exact distance from the platform, so the the tub sits on the platform properly.

From the factory, ours was not causing flex and cracks.

It took us two tubs to figure that out. If it was not for the help found here, we might never had found it.

I think it makes sense to replace the tub if you can get a new one. That way you can make sure it is properly supported underneath. Otherwise, you'll be fixing it from now on out. :)

"Why"...poor support under the tub, resulting in too much flex ? Too much weight in the tub ? Inferior materials ?

"How to fix"...you must find out what the tub is made of in order to find a product to repair it with. And, there may not be a method to fix it, is it easier to replace it? I once used a shower/tub combo in my home, purchased from Lowes, I managed to put a hole in it, called the manufacturer for a repair kit....could not be repaired according to the representative...but the good news is: "it has a lifetime warranty...I'll send you a replacement free of charge"...so I'd start with the RV manufacturer and backtrack to the tub vendor.

Regards
Gemstone